Boiko O. Orientation character of lyotropic chromonic nematic liquid crystals.

Thesis for candidates's degree in Physics and Mathematics on the speciality 01.04.15 - Molecular and Liquid Crystals Physics, Institute of Physics, National Academy of Sciences of Ukraine, Kyiv, 2011. In the manuscript, the basic physical mechanisms for orientation of lyotropic chromonic liquid crystals (LCLC) are considered. The effective and simple method has been proposed for studying the energy of thermal desorption of liquid crystal materials from the substrate surface. It was demonstrated experimentally that bare solid surfaces with adsorbed organic molecules can orient liquid crystals after UV irradiation. The universal reason for the photoinduced anisotropy in such systems is that UV photons selectively remove the molecules which absorb light most effectively thus creating in-plane anisotropy in the adsorbed molecular layer. New effect of photoinduced reorientation of the director in a light-absorbing LCLC is observed. The highly ordered solid films, obtained from LCLC, has been studied and charactarized. It was experimentally demonstrated that the surface anchoring potential in the chromonic system cannot be approximated by the classic Rapini-Papoular model but instead is a discontinuous function of the director deviation from the easy axis and can be described by a double-well anchoring potential with two minima corresponding to tangential and homeotropic orientation. Keywords: lyotropic chromonic nematic liquid crystals, surface anchoring potential, elastic constants, order parameter.